In many areas the need for an accurate measurement and/or characterization of a series of physical parameters of liquids and gases, referred to hereinafter as mobile media, has become more and more evident. The rapid development in recent years of electronic semi-conductor components has led to very powerful, fast, and inexpensive personal computers that replace in many applications where minicomputers were required. Future uses and developments of measuring, control and regulating systems are limited more through the lack of suitable measurement transmitters than of access to computer power. It does not make sense to attempt controlling an industrial process on a per mil level if the available measurement transmitter only has an accuracy of 10%.
While it is possible to measure simple parameters such as electric voltage, current, length, weight etc. with high accuracy, it is not as easy to obtain access to accurate transmitters for the measurement of more complex material properties such as lubricity, flowability, thixotropy, assessment of the quality of paper pulp etc. In the latter areas, human senses often perform better than the foremost measuring system of the day. An experienced process engineer frequently is able by the visual appearance and feel of a paper pulp to assess its suitability. Correspondingly, a physician, simply by talking to a patient, can sense whether the patient is healthy or sick, without being able directly to point to a primary reason for his feeling.
Insofar as transmitters for the type of measuring problem mentioned above are concerned, it is often not possible to specify exactly which properties of the measuring object it would be desirable to measure. More important than the absolute measuring accuracy the measurement transmitter should be consistent and, in a given measuring situation, should always provide the same measured value. Other desirable characteristics of the measurement transmitter are that it must not have a negative effect on the measuring process, and that it should be possible to carry out the measurement by means of a telemetering technique. Finally, the price of the transmitter is always important, though not wholly decisive.
For example, in the foodstuff or processing industry the need exists for continuous monitoring of the flowability or viscosity of the foodstuff product during the course of the process. The prior measurement of the viscosity is a relatively cumbersome method of analysis which involves withdrawing a sample from the process and placing it e.g. in a rotating cylinder viscosimeter. Other analyses may require the determination of the quantity of solid particles in a liquid, where the sample has to be evaporated so that the quantity of solid substance can be weighed. In many cases it is impossible for practical reasons to withdraw a sample for closer analysis. In many biotechnical processes, e.g. fermentation, the process vessel often is a closed container. To allow keeping the production at a high and even level, a continuous checking of how the process develops inside the closed vessel is desirable.
Mass production industries may experience breakdowns resulting in products of reduced quality. In such a situation, it would be desirable to rapidly and reliably separate out the faulty products from the production. It will then not be a matter of just one single point of measurement, but may involve e.g. millions of packages of non-returnable packages of milk. Naturally, it is not possible in this situation to open all packages. Rather the measuring method for the assessment of the contents should function through the unbroken package.
Against the background of the risk of many infectious diseases, such as AIDS, it may be expected that an increasing part of blood transfusions to patients with a need for blood will take place by means of so-called autologous blood transfusion. This means that before an operation patients provide their own blood which is then stored e.g. in plastic bags in cold storage, until it is needed. It will be necessary in such cases to be able to check the quality of the stored blood without opening the bags. The equipment for this purpose naturally has to be subjected to very stringent environmental requirements, e.g. sterilization.